CN111564274A

CN111564274A - Single crystal magnetic powder and its magnetic rheologic fluid and method

Info

Publication number: CN111564274A
Application number: CN202010167069.9A
Authority: CN
Inventors: 梁燕玲; 秦浩
Original assignee: Hunan Bohai New Materials Co ltd
Current assignee: Shenzhen Bohai New Material Technology Co ltd
Priority date: 2020-03-11
Filing date: 2020-03-11
Publication date: 2020-08-21

Abstract

The invention relates to single crystal magnetic powder, magnetorheological fluid and a method thereof. Specifically, the invention provides a magnetorheological fluid containing single crystal magnetic powder, which comprises: monocrystalline magnetic powder; and a fluid used as a carrier liquid, wherein the single crystal magnetic powder is dispersed in the fluid. Compared with the traditional magnetorheological fluid, the magnetorheological fluid containing the single crystal magnetic powder prepared according to the invention has huge irreplaceable advantages, such as higher magnetic saturation strength, higher working shear stress under the same magnetic field strength, quicker response, uneasy sedimentation, low viscosity, low wear rate to components, long service life, high reliability, quicker response and the like.

Description

Single crystal magnetic powder and its magnetic rheologic fluid and method

Technical Field

The present invention relates to the field of magnetorheological fluids. More particularly, the present invention relates to single crystal (monocrystalline) magnetic powder and magnetorheological fluids prepared therefrom. The invention also relates to a method for preparing a magnetorheological fluid containing single crystal magnetic powder.

Background

Magnetorheological fluids are liquids whose viscosity changes with the application of a magnetic field. The stable suspension system is formed by uniformly dispersing soft magnetic particles with high magnetic conductivity and low remanence in a non-magnetic carrier liquid through the action of a surfactant. The working principle of the magnetorheological fluid is as follows: under the action of an external magnetic field, each particle is polarized into a magnetic dipole, the dipoles attract each other, and a chain-bundle-shaped structure formed between the two magnetic pole plates is transversely arranged between the pole plates like a bridge, so that the normal flow of fluid is blocked, and the solid-like characteristic is generated. When the external magnetic field is removed, the fluid returns to the original state, namely the magnetorheological fluid is rapidly and reversibly switched between the liquid state and the solid state. The solid stating degree and the current intensity form a stable and reversible relation, namely the shear yield strength of the solid-stating magnetorheological fluid can be accurately controlled by controlling the current intensity.

Magnetorheological fluids have been used for many years to control damping forces in a variety of devices, such as shock absorbers, body prostheses, and flexible seats. The rheology of the magnetorheological fluid under the action of the magnetic field is instantaneous and reversible, and the shear yield strength after the rheology and the magnetic field strength have a stable corresponding relationship, so that the intelligent control is very easy to realize. Therefore, the magnetorheological fluid is an intelligent material with wide application and excellent performance, and the application field of the magnetorheological fluid is rapidly expanded.

One essential drawback of existing magnetorheological fluids is that the magnetic particles in the fluid are of the polycrystalline type, whether commercially available or single crystal magnetorheological fluid products of the applicant's prior invention. Polycrystalline bodies are crystals in a whole block, are composed of a large number of crystal grains, cannot penetrate through the whole crystal by a space lattice pattern, and have the basic characteristic of magnetocrystalline isotropy. The deficiencies of the prior art in which such polycrystalline magnetic powders having magnetocrystalline isotropy have a slower response speed to magnetic fields and lower magnetic saturation than magnetocrystalline anisotropic magnetic particles in magnetorheological fluids enable the present invention to provide a significant improvement over the prior art in this respect.

Another drawback of the known magnetorheological fluids is that the products available on the market have a less satisfactory shear yield strength, require a higher operating current and possibly more than two excitation coils, making the control of the equipment more complex and costly.

The traditional magnetorheological fluid adopts polycrystalline magnetic powder, which has lower magnetic saturation strength than that of the polycrystalline magnetic powder, low magnetic force under a magnetic field and low shearing force of the magnetorheological fluid. In order to increase the working shear force of the magnetorheological fluid, the magnetic particles of the conventional magnetorheological fluid have a particle size of more than 0.1 μm, preferably more than 1 μm, (see US6203717B1, etc.), which brings about another outstanding problem that the magnetic particles are prone to settle in the magnetorheological fluid.

One of the reasons that particles tend to settle is that the density of oil (0.7-0.95g/cm3) differs greatly from the density of metal particles (iron particles are about 7.86g/cm3) and the other is that the magnetizable particles in conventional magnetorheological fluids are relatively large in size (preferably larger than 1 μm, i.e. 1000 nm, as in US6203717B1 and the like), for example, the prior art magnetic powder particles are mostly around 2-5 microns in size (see the drawings), and are spherical, spheroidal, and chain-spheroidal in shape. The free settling end velocity of a fine solid particle in a fluid medium is proportional to the square of its particle size. The particle materials with excessively large particle sizes settle more quickly and more easily, resulting in non-uniform distribution of particles and interfering with the activity of the magnetorheological fluid. Some of the early magnetorheological fluids (see US 2575360, 2661825, 2886151, US6203717B1, etc.) were based on iron powder and low viscosity oils, all of which tended to settle and the rate of settling accelerated with increasing temperature. It is often necessary to add various thickening and suspending agents. Due to the addition of a large amount of these anti-settling components, the viscosity of the magnetorheological fluid is greatly increased, but at the same time, the flow resistance (viscosity) of the material in a magnetic field-free state is increased.

The settling of the magnetic particles directly results in a short service life, low reliability of the magnetorheological fluid and ultimately failure of the magnetorheological fluid.

The initial viscosity and flow resistance of magnetorheological fluids are high, which directly results in poor performance of parts of equipment, such as moving parts or devices, when no magnetic field is applied.

Another significant technical problem with existing magnetorheological fluids is wear. The magnetic particles in the magnetorheological fluid cause wear on the surfaces of the moving parts with which they come into contact, and the larger the size of the magnetized particles, the more abrasive particles wear.

Another drawback of existing magnetorheological fluids is that commercially available magnetorheological fluid products have deficiencies and room for improvement in both consistency of performance and product performance degradation time.

In view of the above and other considerations, there is a need in the art for further improved magnetorheological fluids and methods and apparatus for making the same that overcome the deficiencies in the prior art.

Disclosure of Invention

In order to solve the problem of magnetocrystalline isotropy of magnetic powder in the prior art, the defects of easy sedimentation of larger magnetic particles in magnetorheological fluid products in part of the prior art, resulting in use effect, service life and the like, and the problem of over-thick initial viscosity of magnetorheological fluid products in part of the prior art, the inventor proposes and realizes the application of single crystal magnetic powder in the preparation of magnetorheological fluid, so that the provision of the magnetorheological fluid containing single crystal magnetic powder in industrial production becomes possible, and the invention can be used for solving the essential defects of polycrystalline magnetic powder and other defects in the prior art. The invention also discloses equipment and a method for preparing the magnetorheological fluid containing the single crystal magnetic powder.

The single crystal magnetic powder has higher specific magnetic saturation strength, and can generate higher magnetic force than the traditional polycrystalline magnetic powder under the same magnetic field, so that the magnetorheological fluid obtains larger shearing force.

The basic principle of the single crystal magnetic powder of the magnetorheological fluid is that the magnetic powder contained therein is single crystal particles, i.e. there is only one lattice type in a single magnetic powder. The single crystal is a crystal with the same atomic arrangement rule and the same crystal lattice phase. The basic structure of a single crystal is characterized in that the entire crystal is composed of either a single crystal grain or a plurality of crystal grains having the same crystal lattice and the same crystal orientation. Thus, the entire crystal lattice of the single crystal is continuous, i.e., a spatial lattice pattern can be used throughout the single crystal, whether the single crystal is composed of one or more grains. The single crystal magnetic powder makes it possible to realize magnetocrystalline anisotropy, thereby solving the above-mentioned drawbacks of the prior art and others.

In a single crystal of a magnetic material, anisotropy of atomic arrangement causes it to have magnetic anisotropy. The measured magnetization curves of the single crystal body magnetized in different crystal axis directions and the ease of magnetization to magnetic saturation are different from each other. That is, a single crystal is easily magnetized in some crystal axis directions and is not easily magnetized in some crystal axis directions, and this phenomenon is called magnetocrystalline anisotropy. For a body-centered cubic (bcc) crystal, for example, the easy magnetization axis is the [100] axis direction and the hard magnetization axis is the [111] axis direction.

According to an example of the present invention, the prepared single crystal anisotropic magnetic powder is a body-centered cubic single crystal, and each magnetic powder or most of the magnetic powders in the magnetorheological fluid base liquid is a body-centered cubic single crystal. In the magnetorheological fluid base fluid, the single crystal magnetic powder is in a free dispersion state, under an external magnetic field, the single crystal magnetic powder is rapidly arranged around the direction of an easy magnetization axis (100 axis) in a rotating manner, namely, the maximum magnetic saturation direction of the material is presented, and the magnetic saturation magnetization is presented in the direction, so that the material has very high magnetic saturation intensity, for example, the magnetic saturation intensity of the single crystal magnetic powder used in one example of the invention can be up to 245emu/g, and the shearing force of the magnetorheological fluid prepared by applying the single crystal magnetic powder under the same magnetic field is far higher than that of the traditional polycrystalline magnetic powder magnetorheological fluid.

Throughout this patent application, it will be understood by those skilled in the art that "particle size" is intended to be used to indicate and characterize the size of the particles. Unless otherwise specified, "particle size" refers to its "particle size" if the particles have a substantially spherical microscopic shape. Unless otherwise specified, "particle size" refers to "equivalent particle size" if the particles have a microscopic shape that is not spherical.

Compared with the traditional magnetorheological fluid, the magnetorheological fluid material containing the single crystal magnetic powder prepared by the invention has the following advantages:

a. higher than magnetic saturation (as shown in FIG. 7)

b. At the same working shear strength requirement, we can use finer powders, which are less prone to sedimentation (as shown in FIG. 8)

The free settling end velocity of a fine solid particle in a fluid medium is proportional to the square of its particle size. In order to reduce residual magnetism, the particle size of the traditional magnetic response particles can reach more than 1 mu m, the particle size of the material is far smaller than that of magnetic powder of the traditional magnetorheological fluid, the material is not easy to settle, and the problem that the magnetic response particles in the traditional magnetorheological fluid are easy to settle is solved. The less prone to sedimentation of the magnetic particles in the magnetorheological fluid of the invention is preferably at least 50%, preferably at least 60%, more preferably at least 80%, most preferably at least 90% of the magnetic particles that do not sediment in the magnetorheological fluid for a period of more than 3 days, preferably more than 1 week, more preferably more than 1 month, most preferably more than 2 months or even longer at room temperature (25 degrees celsius).

c. Is beneficial to realizing the miniaturization and the light weight of the device

The magnetorheological fluid prepared from the single crystal magnetic powder can obtain higher working shearing force than the traditional polycrystalline magnetic powder with the same granularity under the same working magnetic field, so that the excitation part of the device can be miniaturized and lightened.

d. Reducing wear rate to components

The effect of the finer single crystal magnetic powder particles on scratching, cutting and abrading the component is significantly less than that of the coarser powder particles.

e. The single crystal magnetic powder has higher magnetic saturation strength, the proportion of the magnetic powder required by the shearing force reaching the same requirement is low, the initial viscosity can be adjusted to be lower according to the requirement, and the adjustment range is larger. Because the single crystal magnetic powder can be finer and the settling rate is low, the initial viscosity can be reduced without adding a large amount of high viscosity anti-settling component into the carrier liquid (as shown in fig. 10).

f. Good thermal stability

The magnetorheological fluid material containing the single crystal magnetic powder prepared according to the invention has good thermal stability. (see FIG. 9)

According to one embodiment of the present invention, a single crystal magnetorheological fluid and a method of making the same are disclosed. The magnetorheological fluid is prepared by mixing and stirring monocrystalline magnetic powder, carrier liquid, additives and the like. The single crystal magnetorheological fluid prepared by the method can realize the following technical advantages: obtaining larger working yield strength and faster magnetic response speed; smaller single crystal grain size, greatly increased resistance to settling (compared to prior art magnetorheological fluids); the miniaturization and the light weight of the device can be realized.

According to one embodiment of the invention, a single crystal magnetic powder for a magnetorheological fluid is disclosed, consisting of separated single crystal structure magnetizable magnetic particles, the magnetic particles of the single crystal magnetic powder having an average particle size in the range of about 0.1-8 microns; wherein a single said magnetic particle consists essentially of a single crystal grain, or consists essentially of a plurality of crystal grains having the same crystal lattice and uniform crystal orientation.

According to an embodiment of the invention, the material of the magnetizable magnetic particles is selected from pure iron, iron-aluminum alloys, iron-silicon alloys, iron-cobalt alloys, iron-nickel alloys, iron-vanadium alloys, iron-molybdenum alloys, iron-chromium alloys, iron-tungsten alloys, iron-manganese alloys, iron-platinum alloys, iron-copper alloys, nickel, cobalt, SmCo, NdFeB, stainless steel, silicon steel and combinations thereof.

According to an embodiment of the invention, the single crystal of the single crystal magnetic powder has one of the following crystal lattices: hexagonal lattice, cubic lattice, rhombohedral lattice, and body centered cubic lattice.

According to an embodiment of the present invention, the single crystal magnetic powder is a single grain crystal having a characteristic of magnetocrystalline anisotropy.

According to an embodiment of the present invention, there is provided a magnetorheological fluid containing single crystal magnetic powder, comprising: the single crystal magnetic powder as described above; and a fluid used as a carrier liquid, wherein the single crystal magnetic powder is dispersed in the fluid.

According to an embodiment of the invention, the magnetic particles of the single crystal magnetic powder have an average particle size of between about 0.1 and 8 microns, preferably between about 0.8 and 3 microns, more preferably between about 0.8 and 1.5 microns, wherein the number of magnetic particles having an average particle size of between about 0.8 and 1.5 microns preferably comprises more than 50% of the total magnetic particles.

According to an embodiment of the invention, the fluid is an organic liquid, such as an alpha-olefin, a cycloalkane, a saturated alkane, or a combination thereof.

According to an embodiment of the invention, the fluid further comprises an additive selected from the group consisting of surfactants, dispersants, anti-settling agents, organic thixotropic agents, thickeners, antioxidants, lubricants, viscosity modifiers, flame retardants, organoclay-based rheological additives, sulfur-containing compounds, and combinations of these additives.

According to an embodiment of the invention, the volume of the magnetic particles of the single crystal magnetic powder is more than 0.5%, preferably 1-70%, more preferably 10-30% of the total volume of the magnetorheological fluid.

According to an embodiment of the invention, the microscopic shape of the single crystal magnetic powder is selected from the group consisting of substantially spherical, substantially cylindrical, substantially ellipsoidal, substantially prismatic, substantially rectangular parallelepiped, substantially truncated pyramid, substantially rectangular parallelepiped with steps, or prismatic, or any combination thereof.

According to an embodiment of the invention, the magnetic particles of single crystal magnetic powder are substantially free of sedimentation stratification during standing in the magnetorheological fluid containing single crystal magnetic powder at room temperature for a period of at least 1 week, preferably at least 2 weeks, more preferably at least 1 month.

According to an embodiment of the present invention, the microscopic shape of the single crystal magnetic powder exhibits a specific geometrical configuration according to its single crystal structure and main growth crystal orientation.

According to an embodiment of the invention, at least 50% by volume, preferably at least 60% by volume, more preferably at least 80% by volume, most preferably at least 90% by volume of the single crystal magnetic powder substantially does not settle during the standing of the magnetic particles of the single crystal magnetic powder in the magnetorheological fluid containing single crystal magnetic powder at room temperature for 1 month.

According to an embodiment of the present invention, there is provided a method for producing a magnetorheological fluid containing single crystal magnetic powder, comprising: providing a precursor in the form of an oxide for preparing the single-crystal magnetic powder, wherein the precursor contains iron element and at least one element selected from the group consisting of aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, platinum, copper, boron and samarium; carrying out chemical reduction and recrystallization on the precursor in a reducing atmosphere to obtain the single crystal magnetic powder; adding the raw material of the single crystal magnetic powder, the additive and a part of carrier liquid into a primary mixer together, and mixing and dispersing to obtain primary slurry; further screening and separating the primary slurry to obtain slurry containing the required single crystal magnetic powder, wherein the screening and separating comprises at least one of gravity separation, centrifugal separation and magnetic separation; and selectively adding carrier liquid and additives into the material containing the required single crystal magnetic powder in a stirrer and stirring to obtain the magnetorheological fluid containing the single crystal magnetic powder.

According to an embodiment of the present invention, the additive comprises at least one of an antioxidant, an anti-settling agent, and a dispersant.

In accordance with the present invention, the use of a magnetorheological fluid containing single crystal magnetic powder for vibration damping and/or cushioning in load bearing applications including at least one of vehicles, engineering machinery, processing machinery, medical equipment, bridges, and drilling platforms is disclosed. The applicable vehicles include various light and heavy cars, trucks, boats and civil aircrafts. The engineering machinery comprises various mining vehicles, hoisting equipment, excavators, drilling machinery and the like.

The magnetorheological fluid of the present invention is applicable to, but not limited to, dampers, bumpers, shock absorbers, human prostheses and elastic seats, brakes, e.g., bumpers for automobiles, automobile shock absorbers, precision machining equipment such as machine tool bumpers, high speed train bumpers, and the like.

Compared with the traditional magnetorheological fluid, the magnetorheological fluid containing the single crystal magnetic powder has huge irreplaceable advantages, such as higher shear yield strength, uneasy sedimentation, low viscosity, low wear rate to components, long service life, high reliability, quick response, excellent thermal stability and other performance advantages.

Drawings

The features, objects, and advantages of the present invention will become more apparent from the description set forth below when taken in conjunction with the drawings in which:

FIG. 1 schematically illustrates an apparatus for preparing a single crystal magnetorheological fluid according to one embodiment of the invention.

Fig. 2 schematically shows in plan view the apparatus for preparing a single crystal magnetorheological fluid shown in fig. 1.

Fig. 3 is a Scanning Electron Microscope (SEM) photograph of single crystal magnetic powder particles according to an embodiment of the present invention at 10000 times magnification.

Fig. 4A is a Scanning Electron Microscope (SEM) photograph of single crystal magnetic powder particles according to an embodiment of the present invention at 10000 times magnification.

Fig. 4B is a Scanning Electron Microscope (SEM) photograph magnified 10000 times by commercially available magnetic powder particles as a comparative example.

Fig. 5 is a comparison graph of hysteresis loop test of single crystal magnetic powder according to an embodiment of the present invention with nano magnetic powder of the applicant's previous invention and commercially available conventional magnetic powder, showing hysteresis loop test comparison of magnetic powder.

FIG. 6 is a comparison of hysteresis loop measurements of single crystal magnetic powder and commercially available magnetic powder of one embodiment of the present invention.

FIG. 7 is a comparison of the shear force measurements at the same ratio of a single crystal magnetic powder of an embodiment of the present invention to a commercially available magnetic powder.

Fig. 8 shows that the single crystal magnetorheological fluid of an embodiment of the present invention achieves a shear force of 72% magnetic particle concentration of the conventional magnetorheological fluid at 50% single crystal magnetic particle concentration, showing that the 50% magnetic particle concentration of the single crystal magnetorheological fluid achieves a shear strength of 72% magnetic particle concentration of the conventional magnetorheological fluid.

FIG. 9 shows the thermal stability of a single crystal magnetorheological fluid in accordance with an embodiment of the invention.

FIG. 10 shows a comparison of the single crystal magnetic powder of an embodiment of the present invention and a conventional polycrystalline magnetic powder under the same particle size, the same concentration, and the same magnetic field for the shear force test.

FIG. 11 shows a comparison of the settling rate of a single crystal magnetorheological fluid of one embodiment of the invention and a conventional magnetorheological fluid after standing.

Detailed Description

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

Several specific embodiments of the present invention will be described in more detail below.

Before further describing embodiments of the present invention, the inventors intend to explain several terms of the present invention as follows.

The term "anisotropic" refers to a property in which all or part of the chemical, physical, etc. properties of a substance change with a change in direction, and exhibit differences in different directions. Anisotropy is a property that is common in materials and media. The term "magnetic anisotropy" refers to the phenomenon that the magnetism of a substance varies with direction, and is mainly represented by the change of the magnetic susceptibility of a weak magnet and the change of the magnetization curve of a ferromagnetic body with the magnetization direction. The magnetic anisotropy of a ferromagnet is particularly prominent, and is one of the fundamental magnetic properties of a ferromagnet, which means that the free energy density differs at different crystal directions for saturation (or spontaneous) magnetization. Typical magnetic anisotropy arises from the anisotropy of the magnetic crystal.

In the context of the present invention, "magnetic anisotropy" enables magnetic particles to be bonded into chains more rapidly with stronger bonding force and torsion resistance after application of a magnetic field, to respond more rapidly to an applied magnetic field, and to be restored more rapidly to the original state before the applied magnetic field is removed, as compared to isotropic magnetic powders.

The different magnetocrystalline structures of the magnetic powder particles have a significant influence on the properties of the magnetic powder particles after application of a magnetic field, such as the responsiveness and the fast chain formation and the torsion resistance. Magnetic powder particles having an anisotropic magnetocrystalline structure can provide more superior properties in terms of, for example, responsiveness and rapid chain formation properties, torsional strength, etc., as compared with an isotropic magnetocrystalline structure. For example, anisotropic magnetocrystalline structures, such as hexagonal, partially cubic, rhombohedral, and the like, are preferred because they provide significantly improved performance upon application of a magnetic field.

The inventors of the present invention have surprisingly found that the crystal structure of body-centered cubic (bcc), although it can be considered as generally isotropic, has an easy axis of magnetization in the bcc lattice structure, and thus a single crystal magnetic powder of the bcc lattice structure is easily magnetized along the easy axis of magnetization, and thus can be considered as magnetically anisotropic in terms of magnetization, capable of exhibiting magnetic anisotropy, and thus possessing various advantages of anisotropic magnetorheological fluids. Therefore, a magnetic material (magnetic particle) having a body-centered cubic (bcc) single crystal structure is preferable for the present invention.

Selection of magnetic powder (magnetic particle) material

Any solid known to have high magnetic saturation can be used in the present invention, including in particular paramagnetic and ferromagnetic elements and compounds. For example, examples of suitable magnetizable particles include iron, iron alloys (alloying elements include aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, and/or copper), iron oxides (including Fe)₂O₃And Fe₃O₄) Iron nitride, iron carbide, carbonyl iron, nickel, cobalt, chromium dioxide, stainless steel, and silicon steel. Examples of suitable particles include, for example, pure iron powder, reduced iron powder, a mixture of iron oxide powder and pure iron powder. Preferred magnetic-responsive particles are pure iron and iron-cobalt alloys.

Selection of carrier liquid

The carrier liquid constitutes the continuous phase of the magnetorheological fluid. Non-volatile, non-polar organic oils may be used as the carrier component, and examples of suitable carrier liquids include silicone oils, hydraulic oils, motor oils, gearbox oils, alpha-olefins, and the like. The carrier liquid also contains additives such as organoclays, organic thixotropic agents, anti-settling agents, metal soaps, and other additives, as described in more detail below.

1. Organic clay and organic thixotropic agent

The viscosity and sagging property of the magnetorheological fluid can be controlled by adding the organic clay and the organic thixotropic agent, and the sedimentation of magnetizable particles is delayed. Examples of the organic clay that may be selected include tallow bentonite, ammonium salt of 2-methyl-2-hydrogenated tallow brucite. Optional organic thixotropic agents may be Advitrol 100 rheology additives and thixatrol st, Rheox 1 rheology additives, and the like.

2. Anti-settling agent

Anti-settling agents are added to prevent settling of the nano magnetizable particles, and optional anti-settling agents include M-P-A2000X, M-P-A60X anti-settling agent or Y-25, Y-40, YPA-100 anti-settling agent, and the like.

3. Thickening agent

Thickeners may include metal soaps, aluminum stearate, aluminum (iso) octoate, and calcium linoleate in slurry form, which together with the solvent create a gel structure that improves the suspension of the magnetorheological fluid.

4. Other additives

Other additives may also be added, including antioxidants, lubricants, etc., depending on the application of the magnetorheological fluid.

In the present invention, the magnetic particles in the magnetorheological fluid are in a non-settling state, and in this regard, the term "non-settling" should be understood to mean that no significant or substantial settling occurs in the magnetic particles in the magnetorheological fluid not only during the pauses between the operating states of the magnetorheological fluid, but also in the natural rest state of the magnetorheological fluid, e.g., at about 25 ℃ room temperature.

More precisely, a so-called "less prone to sedimentation" state in the present invention is considered to be reached if at least 50%, preferably at least 60%, more preferably at least 80%, most preferably at least 90% of the magnetic particles in the magnetorheological fluid do not sediment during more than 3 days, preferably more than 1 week, more preferably more than 1 month, most preferably more than 2 months or even longer of standing of the magnetorheological fluid in the natural standing state at room temperature.

The single crystal magnetic powder and the process for producing the same according to the present invention will be further described with reference to the accompanying drawings in conjunction with an embodiment.

Preparing metal or alloy oxides

An iron-cobalt alloy powder (for example, iron: cobalt ═ 2:1) of less than 100 mesh is purchased, and the iron-cobalt alloy powder is calcined at a high temperature (about 600 to 1000 ℃) in an oxidizing atmosphere to obtain a cobalt oxide-iron oxide mixture. The ratio of iron to cobalt in the iron-cobalt alloy powder may be any ratio, such as 1:1, 7:3, 3:7, 2:8, etc., depending on the desired properties of the single crystal magnetic powder of the final product. And, other elements, such as Mn, Ni, Cr, etc., may be added to the iron-cobalt alloy powder in a certain ratio according to desired properties of the single crystal magnetic powder of the final product. It will also be apparent to those skilled in the art that the composition of the alloy powder may be other ferromagnetic alloy powders containing more than two metal components.

Ball milling and screening

The resulting mixture of iron oxide and cobalt oxide is fed to a commercially available ball mill, for example a model JQM series ball mill, and ball milled for 24-48 hours at a ball mill ball to powder ratio of 1:1, ball-milling the mixture with a filling coefficient of 50 percent and a rotating speed of 70 percent of critical rotating speed to obtain crushed materials, and then primarily screening the crushed materials through a 60-100 mesh screen to obtain a precursor of the iron oxide and cobalt oxide mixture.

Chemical reduction and crystallization

According to a preferred embodiment, a reducing atmosphere containing 20-100% hydrogen plus 80-0% nitrogen is used. The above precursors were charged into a commercially available chemical reduction reactor for industrial use. Wherein, the loading amount is 5 Kg; gas flow rate of reducing atmosphere: 1.5-5L/min; reaction time: 30-80H; temperature setting: 520 ℃ and 720 ℃; then, the mixture was cooled to room temperature in a reducing atmosphere to obtain a single-crystal iron-cobalt alloy powder. It will be appreciated by those skilled in the art that the various parameters described above may be adjusted and varied depending on the composition, desired properties, grain size, etc.

Testing of single crystal magnetic powder: the single crystal magnetic powder of the present invention is scanned and tested using various conventional testing equipment such as a scanning electron microscope, a specific saturation magnetization tester, a shear force testing equipment, and the like.

FIG. 3 is a Scanning Electron Microscope (SEM) photograph at 10000 times magnification of single crystal magnetic powder particles prepared according to an embodiment of the invention, showing the morphology of the single crystal magnetic powder particles at that magnification; FIG. 4A is a Scanning Electron Microscope (SEM) photograph at 10000 times magnification of single crystal magnetic powder particles of another size range according to an embodiment of the invention, showing the morphology of the single crystal magnetic powder particles at that magnification; fig. 4B is a Scanning Electron Microscope (SEM) photograph of 10000 times magnified from commercially available magnetic powder particles of a comparative example to be compared with the present invention. Fig. 3-4A show different sizes and morphologies of single crystal magnetic powder particles prepared according to the present invention. It can be seen that the overall size distribution of the single crystal magnetic powder is uniform, the morphology is regular and controllable, and the particle size is much smaller than that of the existing polycrystalline magnetic powder as a comparative example in fig. 4B. As mentioned above, this clearly contributes to the basic anti-settling properties of magnetorheological fluids, and the consistency and reliability of the product is more controllable and easier to achieve.

FIG. 5 is a comparison of hysteresis loop test of single crystal magnetic powder of one embodiment of the present invention with applicants' previously invented nano magnetic powder and commercially available conventional magnetic powder. FIG. 6 is a comparison of hysteresis loop measurements of single crystal magnetic powder and commercially available magnetic powder of one embodiment of the present invention. As can be seen from FIGS. 5-6, the performance index parameters of the single crystal magnetic powder of the present invention in terms of magnetic saturation strength, remanence and coercivity are far superior to those of the magnetic powder in the conventional magnetorheological fluid.

Magnetorheological fluid prepared from single crystal magnetic powder

Referring to fig. 1 and 2, fig. 1 is a schematic perspective view of a mixing-separating apparatus for mixing and separating single-crystal magnetic powder and a carrier liquid according to an embodiment of the present invention, and fig. 2 is a schematic plan view of an embodiment of the mixing-separating apparatus shown in fig. 1.

As shown in fig. 1-2, an embodiment of the apparatus for producing a magnetorheological fluid containing single crystal magnetic powder according to the invention comprises a primary mixer 1, a sedimentation separator 2, a magnetic separator 3, a pump 5, a stirrer 4, wherein the sedimentation separator 2 is preferably located downstream of the primary mixer 1 and connected to the primary mixer 1 by a line 6, and the magnetic separator 3 is preferably located downstream of the sedimentation separator 2 and also connected to the sedimentation separator 2 by a line. Wherein the magnetic separator 3 and the sedimentation separator 2 are preferably provided with an outlet and a primary mixer 1, respectively, so that the undesirable raffinate is selectively returned to the primary mixer 1 for reprocessing by means of a pump 7.

A blender 4 is preferably located downstream of the magnetic separator 3 and is also connected to the magnetic separator 3 by a line for receiving the fluid containing the desired single crystal magnetic powder particles from the magnetic separator 3.

The single crystal iron-cobalt alloy powder and the carrier liquid of the selected magnetorheological fluid are primarily stirred and mixed in a primary mixer 1 to disperse the single crystal iron-cobalt alloy powder. The carrier liquid may, for example, employ alpha-olefins as grinding media. In the primary mixing step, a surfactant may be added, which may also act as a dispersant to prevent the single crystal magnetic powder from agglomerating and welding. For example, in this regard, the following example may be taken.

According to example 1, 30g/l of single crystal magnetic powder is provided, the carrier liquid is 28.05g/l of alpha-olefin, 1.2g/l of antiwear agent, 0.3g/l of dispersant, and 0.45g/l of antioxidant. The carrier liquid and various additives are stirred at a low speed of 300r/min for 10min, the single crystal magnetic powder is added, and stirring is carried out at 1200r/min for 20min, thus preparing the slurry of the primary mixed material of the single crystal magnetorheological fluid with the magnetic powder ratio of about 72%.

According to example 2, 30g/l of single crystal magnetic powder is provided, the carrier liquid is 28.05g/l of alpha-olefin, 1.2g/l of antiwear agent, 0.3g/l of dispersant, and 0.45g/l of antioxidant. The carrier liquid and various additives are stirred at low speed of 300r/min for 10min, the single crystal magnetic powder is added, and stirring is carried out at 1200r/min for 20min, thus preparing the slurry of the primary mixed material of the single crystal magnetorheological fluid with the magnetic powder ratio of about 50%.

Precipitation separation step

The slurry of the primary mix is transferred to a precipitation separator 2, for example a self-made gravity separator or centrifugal separator (for example model LW50 x 1100), and the desired particle size (for example, a particle size range of about 0.1 to 8 μm, which may vary depending on the particular type of single crystal magnetic powder, process requirements and application requirements) of the single crystal magnetic powder is separated by gravity or centrifugal force and the desired fine particles are transferred to a magnetic separator 3. As an example, single crystal magnetic particles that are not of the desired size or that are still agglomerated may optionally be recycled back to the primary mixer 1 by pump 5 and may be used for re-dispersion and screening, e.g., for another standard, avoiding waste of single crystal material.

According to a preferred embodiment, the slurry of the blend in the gravity or centrifugal separator is heated to a temperature, for example 35-50 degrees Celsius, to facilitate separation.

Magnetic separationSeparation procedure

According to an alternative embodiment, as an alternative or additional process to the gravity precipitation separation or the centrifugal separation process, slurry of single crystal magnetic powder particles having a higher concentration than a predetermined concentration may be separated by the magnetic separator 3 by applying an exciting current to the magnetic powder particles to generate an electromagnetic attraction force, and sent to the stirrer 4 to be subjected to a next stirring process. According to this example, the concentration of the single crystal magnetic powder in the separated slurry can be controlled by controlling the magnitude of the exciting current.

Stirring step

The slurry containing single crystal magnetic powder particles separated from the magnetic separator 3 is characterized by density value for the content of magnetic particles, supplemented with carrier liquid (e.g. alpha-olefin), added with anti-settling agent (e.g. M-P-a2000X, NL chemical company), lubricant (e.g. silicone oil) and optionally defoamer, and stirred by a stirrer 4 (model DX-L500) for about 1 hour to obtain a satisfactory magnetorheological fluid containing single crystal magnetic powder.

Sedimentation test

Test 1

And (3) naturally standing the magnetorheological fluid containing the single crystal magnetic powder at room temperature to test the sedimentation performance of the magnetorheological fluid. Tests show that almost no sedimentation and delamination are observed after the magnetorheological fluid containing the single crystal magnetic powder is naturally kept still for 2 weeks. After standing naturally for 4 weeks, no sedimentation stratification was observed. After standing naturally for 8 weeks, no sedimentation stratification was observed. At least 50%, and even more than 90%, of the magnetic particles in the magnetorheological fluid containing the single crystal magnetic powder do not settle during the period.

Test 2

The magnetorheological fluid containing the single crystal magnetic powder is tested in a constant temperature oven at the set temperature of 70 ℃ and room temperature by adopting a TZC-4 type particle tester produced by Shanghai Fanrui instruments Co., Ltd, the sedimentation height is set to be 3 cm, the time is set to be 180 hours, and the sedimentation degree of the two magnetorheological fluids is expressed by the Ratio (Ratio) of the height of the layered clear liquid to the total height. FIG. 11 shows a comparison of the settling rate (Ratio) of a single crystal magnetorheological fluid and a conventional magnetorheological fluid after standing in accordance with an embodiment of the invention. The figure shows that the single crystal magnetorheological fluid of the present invention is significantly superior to conventional magnetorheological fluids in anti-settling properties.

Shear strength test

The magnetorheological fluids prepared from the single crystal magnetic powder of the present invention and the commercially available conventional magnetic powder were each subjected to shear force examination in an applied magnetic field. An Antopa detection device MRC301 magnetorheological rheological property detector is adopted, the detection parameters are 10-1 of speed, 0-3.6A of detection current, 0-1T of magnetic field and 50 points.

FIG. 7 is a shear force test comparison of a magnetorheological fluid in the same ratio of a configuration of a single crystal magnetic powder of one embodiment of the present invention and a commercially available conventional magnetic powder. It can be seen that under the condition that the magnetic powder concentration is the same (72%) and the same exciting current is applied, the shear strength of the magnetorheological fluid prepared from the single crystal magnetic powder is far better than that of the magnetorheological fluid prepared from the traditional magnetic powder.

FIG. 8 shows that the single crystal magnetorheological fluid of one embodiment of the invention achieves a shear force of 72% magnetic particle concentration of a conventional magnetorheological fluid at 50% single crystal magnetic particle concentration.

FIG. 9 shows the shear strength parameters of a single crystal magnetorheological fluid in accordance with an embodiment of the invention and a conventional magnetorheological fluid as a comparative example tested at 25℃ and 75℃, respectively. It is clear that the thermal stability of the single crystal magnetorheological fluid of the present invention is also superior to conventional magnetorheological fluids in terms of shear strength.

FIG. 10 shows a comparison of shear forces measured in an applied magnetic field for magnetorheological fluids of the same concentration formulated for single crystal magnetic powder of 2 micron particle size according to one embodiment of the invention and conventional polycrystalline magnetic powder of 2 micron particle size. The graph shows that the shear strength index in this case of the different single crystal magnetorheological fluids of the present invention consistently outperforms the conventional magnetorheological fluids.

Embodiments of single crystal structure magnetic powder, magnetorheological fluid prepared therefrom, and methods and apparatus for making the same of the present invention are described in detail above with reference to the drawings. It will be understood by those skilled in the art, however, that the foregoing is illustrative and descriptive of some specific embodiments only, and is not limiting as to the scope of the invention, particularly the scope of the claims. The scope of the invention is only limited by the appended claims.

Claims

1. A single crystal magnetic powder for a magnetorheological fluid, consisting of separated single crystal structure magnetizable magnetic particles having an average particle size in the range of about 0.1 to 8 microns, preferably between about 0.8 to 3 microns; wherein a single said magnetic particle consists essentially of a single crystal grain, or consists essentially of a plurality of crystal grains having the same crystal lattice and uniform crystal orientation.

2. A single crystal magnetic powder according to claim 1, wherein the magnetizable magnetic particles are of a material selected from the group consisting of pure iron, iron-aluminum alloys, iron-silicon alloys, iron-cobalt alloys, iron-nickel alloys, iron-vanadium alloys, iron-molybdenum alloys, iron-chromium alloys, iron-tungsten alloys, iron-manganese alloys, iron-platinum alloys, iron-copper alloys, nickel, cobalt, SmCo, NdFeB, stainless steel, silicon steel, and combinations thereof.

3. A single crystal magnetic powder according to any one of claims 1 to 2, wherein the magnetic particles of the single crystal magnetic powder are single particle crystals having magnetocrystalline anisotropy characteristics.

4. A magnetorheological fluid containing single crystal magnetic powder, comprising:

the single crystal magnetic powder according to any one of claims 1 to 3; and

a fluid used as a carrier liquid, wherein the single crystal magnetic powder is dispersed in the fluid.

5. The magnetorheological fluid of claim 4, wherein the magnetic particles of the single crystal magnetic powder have an average particle size of between about 0.1 and 8 microns, preferably between about 0.8 and 3 microns, and more preferably between about 0.8 and 1.5 microns, wherein the number of magnetic particles having an average particle size of between about 0.8 and 1.5 microns preferably comprises more than 50 percent of the total magnetic particles.

6. The magnetorheological fluid of any one of claims 4 to 5, wherein the fluid is an organic liquid, such as an alpha olefin, a cycloalkane, a saturated alkane, or a combination thereof.

7. The magnetorheological fluid of any one of claims 4 to 6, wherein the magnetic particles of the single crystal magnetic powder comprise more than 0.5 percent by volume of the total volume of the magnetorheological fluid, preferably from 1 to 70 percent by volume, and more preferably from 10 to 30 percent by volume.

8. The magnetorheological fluid of any one of claims 4 to 7, wherein the magnetic particles of the single crystal magnetic powder are substantially free of settling and delamination upon standing in the magnetorheological fluid at room temperature for a period of at least 1 week, preferably at least 2 weeks, more preferably at least 1 month.

9. Use of a magnetorheological fluid containing single crystal magnetic powder according to any one of claims 4 to 8 for vibration damping and/or cushioning in load bearing applications comprising at least one of vehicles, engineering machinery, processing machinery, medical equipment, bridges and drilling platforms.

10. A method for producing a magnetorheological fluid containing single crystal magnetic powder, comprising:

providing a precursor in the form of an oxide for preparing the single-crystal magnetic powder, wherein the precursor contains iron element and at least one element selected from the group consisting of aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, platinum, copper, boron and samarium;

carrying out chemical reduction and recrystallization on the precursor in a reducing atmosphere to obtain the single crystal magnetic powder;

adding the raw material of the single crystal magnetic powder, the additive and a part of carrier liquid into a primary mixer together, and mixing and dispersing to obtain primary slurry;

further screening and separating the primary slurry to obtain slurry containing the required single crystal magnetic powder, wherein the screening and separating comprises at least one of gravity separation, centrifugal separation and magnetic separation;

and selectively adding carrier liquid and additives into the material containing the required single crystal magnetic powder in a stirrer and stirring to obtain the magnetorheological fluid containing the single crystal magnetic powder.